U.S. Pat. No. 4,497,196 (which is hereby incorporated by reference in its entirety) discloses a stamping and forming machine comprising a plurality of individual modules, each of which contains a set of stamping and/or forming tooling. Strip material is fed intermittently through the machine and during dwell periods the tooling in each of the modules performs an operation on the strip such as blanking, coining, and forming. Machines of the type shown in the above-identified U.S. patent require at least one feeding mechanism for feeding the strip material and where the machine contains a plurality of modules, it is preferable to provide an individual feeding unit for each of the modules.
In any stamping and forming process in which precisely dimensioned parts are being produced, it is essential that the strip be located in each of the die stations with a high degree of precision for the reason that if the feeding operation is not precisely controlled, the articles or parts produced will not be held to close dimensional tolerances. For example, a strip of electrical terminals is commonly produced by feeding strip material through a plurality of die stations so that one operation can be carried out on the strip at each of the stations. The article being produced may be blanked at the first station, partially formed at the second station, coined at the third station, and subsequently subjected to additional forming and other operations. If the resulting terminals are to be manufactured to close dimensional tolerances, it is essential that the partially formed parts be precisely located in each of the die stations with respect to the tooling (punches, forming dies, shearing dies, etc.) in order to maintain precisely controlled dimensions in the finished terminals. Most feeding mechanisms used on stamping and forming machines are incapable of feeding the strip material during each feeding cycle with the precision required for the production of precisely dimensioned parts and it is therefore common practice to use pilot pins in the die assembly which serve precisely to position the strip with respect to the forming tooling after feeding has taken place. The pilot pins may be provided on the die shoe and extend therefrom beyond the ends of the forming tooling (the punches or other tooling). The pilot pins enter pilot holes which are precisely located in the strip and move it by a very slight amount so that it is precisely positioned with respect to the tooling prior to engagement of the tooling with the strip material.
The use of pilot pins in a stamping and forming die assembly requires that the strip be capable of moving a very slight amount when the pilot pins enter the pilot holes. In other words, the strip cannot be held by the feed mechanism or otherwise while the pilot pins are entering the pilot holes for the reason that it would then be impossible for the pilot pins to serve their function of adjusting the position of the strip with reference to the forming tools.
U.S. patent application Ser. No. 057,556, filed June 3, 1987 describes a strip feed mechanism for a multi-station stamping and forming machine in which the strip is fed by a sprocket wheel that is intermittently rotated by means of a suitable geneva mechanism or otherwise to feed the strip. The strip is held against the periphery of the sprocket wheel so that the sprocket teeth will enter the pilot holes in the strip by means of a biasing or holding shoe. The shoe, however, is moved away from the strip during non-feeding intervals so that the strip is released and when the pilot pins enter the pilot holes at an adjacent forming station, the strip is free to move for final and precise adjustment as discussed above. The feeding mechanism described in application Ser. No. 057,556 is being used successfully; however, the mechanism which is employed to hold the shoe against the strip and against the sprocket wheel during feeding intervals and move the shoe away from the sprocket during non-feeding intervals is relatively complex and it has been found that it is not required in all stamping and forming operations. The present invention is directed to the achievement of an improved mechanism for holding the strip material against the sprocket wheel during feeding intervals and releasing the strip material for limited movement during non-feeding intervals so that the pilot pins can precisely position the strip with respect to the tooling.